Iranian Journal of Materials Forming
Volume:7 Issue: 2, Summer and Autumn 2020

The effects of intercritical annealing and subcritical tempering on the mechanical properties and corrosion resistance of mild steel were studied. It was revealed that intercritical annealing followed by quenching resulted in the development of a ferritic-martensitic dual phase (DP) microstructure with high tensile strength, disappearance of the yield-point phenomenon, superior work-hardening behavior, and decreased corrosion resistance. Subsequent tempering of the intercritically annealed steel resulted in the formation of carbide particles in a tempered martensitic microstructure, which led to the decline of the strength and hardness, reappearance of the yield-point elongation, and enhanced corrosion resistance. Accordingly, this work demonstrated the possibility of controlling the mechanical properties and corrosion resistance of commercial mild steels by simple heat treatments.

The flame forming process is widely used to manufacture ship hull plates. The saddle-shaped surfaces have different curvatures in perpendicular angles of planes and the manufacturers face an anti-clastic curvature. In this article, the manufacturing of saddle-shaped surfaces utilizing the flame forming process is investigated. The spiral irradiating scheme is used for forming. In order to study the effects of process parameters (pitch of spiral path, number of irradiation passes, and the movement pattern (In-to-Out or Out-to-In)), several experiments have been carried out. Determining the effect of process parameters for fabrication of this type of sheet leads to the precise manufacturing with reduced costs and lower production time. After the implementation of the experiments, the displacement of the sheet is measured and the saddle-shaped surfaces are manufactured successfully by the spiral irradiating scheme. The final part has large deformations and the curvature can be clearly observed. The deformation of the saddle-shaped surface is noticeably increased by reducing the spiral path pitch (110% increase in height of the center point of the sheet). Also, it is proved that the Out-to-In spiral path movement pattern leads to larger deformations than In-to-Out ones. Besides, the deformations of manufactured saddle-shaped surfaces are increased by increasing the number of spiral passes.

One of the most popular forming processes is the shape rolling process in which the desired shape change is achieved by pressing two rollers with a special shape in the opposite rotational direction. In order to improve the product’s quality and reduce production costs, accurate analysis of the shape rolling process of the compressor blades as well as the investigation of the effective parameters have been done. First, the shape rolling process of a typical compressor blade was simulated based on the experimental data using the finite element method and Design of Experiment (DOE). Then, the effect of various process parameters, including the thickness and width of the preform, the roller diameter, the thickness and width of the flash channel, and the number of the rolling steps on two objectives, namely the rolling force and the amount of the flash were investigated. The obtained data were analyzed by Analysis of Variance (ANOVA), and the contributory factors of the shape rolling process were identified. The results revealed that all of the considered factors affected the rolling load, but only the initial sheet's width and thickness were the factors with impact on the volume of the flash as the second objective. The required process load decreased by increasing the number of the rolling steps, but the rolling load increased by increasing other factors. Furthermore, increasing the thickness and width of the initial sheet increased the flash volume.

The effect of geometrical parameters involved in vortex extrusion (VE) die design, on AA1050 aluminium alloy processed by VE were investigated using finite element analysis (FEA) and response surface methodology (RSM). For this, VE die length (L), reduction in area (RA), twist angle , and position of control points in Beziers' formulation (C1) were considered as input parameters and strain inhomogeneity was considered as a response. Both standard deviation (S.D) and inhomogeneity index (Ci) were used to quantify the strain inhomogeneity from FEA results. Analysis of variance (ANOVA) was used to determine the significant parameters and to mathematically model the strain inhomogeneity. It was concluded that standard deviation (S.D) is not a good choice for examining the strain inhomogeneity distribution in VE technique. ANOVA results showed that , RA, and interaction between  and RA are the most significant parameters affecting the strain inhomogeneity.

In this research, two new methods that improve the drawing depth of deep-drawing processes have been introduced. In the first technique, by creating ridges on the punch surface, the stress concentration is decreased on the blank near the punch edge, in turn increasing the drawing depth. The second method is based on the principle of reducing resistant force in the flange area between the die, the blank-holder and the blank that can decrease the required forming energy. By using the ridges on the flange surfaces of die and blank-holder, the contact surface is reduced, which in turn can decrease the force required for blank forming. The simulation results of finite elements are compared to the experimental data. It is found that the ridged punch may delay the blank rupture and significantly raise the drawability.

Three mm thick plates of commercial pure copper were welded via friction stir welding method using a floating bobbin tool. The effect of different process variables such as the tool transverse speed and the tool rotation speed were examined in order to create a weld with the desired properties. A defect-free weld was obtained at a rotation speed of 1400 rpm and a transverse speed of 18 mm/min with a shoulder pinching gap of 2.7 mm. After the welding process, the soundness of the welds was confirmed by non-destructive methods of visual inspection and X-ray radiography. The results of the transverse tensile test showed that the as-weld joint efficiency was 86.4%, which was higher than the joint efficiency made by the fusion welding method. The strength of the welds was such that the fracture of the workpiece was in the heat affected zone after the tensile test. On the other hand, the grain size of the weld was significantly less than the base metal. The lowest hardness around 40VHN was attributed to the middle of the thickness of the weld, while the highest hardness was in the vicinity of the lower shoulder of the tool, which was about 80 VHN.

Aluminum alloys have a high strength-to-weight ratio and proper anti-corrosion properties that are used in the automotive, shipbuilding and aerospace industries. The major problem with forming aluminum sheets is the low formability of aluminum sheets at room temperature. Therefore, in the present study, warm deep drawing (WDD) of AA5052-O aluminum alloy sheets with a thickness of 1mm was investigated at the different forming temperatures of 25, 80, 160, and 240°C (in the two isothermal and nonisothermal conditions) and punch speeds of 260, 560 and 1950 mm min-1 using experimental tests and finite elements simulation. The finite element simulation predictions show a good agreement with the experimental data. The results showed that an increase in forming temperature and a decrease in forming speed led to a decrease in forming force and an increase in cup height. Additionally, a microstructural and experimental investigation showed that the fracture of the cup corner radii occurs in the early stages of drawing at forming temperature of 25°C whereas, by increasing the forming temperature to higher than 160°C, the drawability of aluminum sheets increases due to dynamic recovery that takes place during the WDD process.

The role of microstructure on hot deformation behavior of sintered Cu-28Zn prealloyed powder compacts was investigated by a series of isothermal hot compression tests in the temperature range of 550- 850°C at strain rates of 0.001, 0.01, 0.1 and 0.5 s-1, by taking into consideration the Hyperbolic Sine functional behavior to analyze the deformation behavior of the alloy. The results indicate that dynamic recrystallization (DRX) has occurred in a large scale. The DRX nucleation sites are along initial grain boundaries, inside the twin bands and triple junctions. In all stress- strain curves in strains more than 0.2 dynamic recovery (DRV) and DRX take place simultaneously. The effect of strain rate and temperature on dynamically recrystallized grain refinement was investigated. Microstructure is in compliance with the results through the Zener-Hollomon relation and has satisfied hot deformation stress- strain curves. This study may provide a new understanding on hot plastic deformation of sintered prealloyed particles microstructure. The results obtained can be used to develop and optimize the conditions of hot plastic deformation of similar prealloyed powder compact.

This study investigates the effect of material parameters of the Gurson-Tvergaard-Needleman (GTN) model on the failure prediction of cellular structures. The effect of elastic modulus, calibration parameter of GTN model, isotropic hardening, fracture strain, and strut diameter on the load-displacement curve of a lattice structure fabricated by Selective Laser Melting (SLM) has been studied by using the finite element method. The power law of Hollomon has been used to model the isotropic hardening behavior. The considered lattice structure is made of AlSi10Mg alloy, which is used in different industries. A 20cm×20cm×20cm structure with 4 Body Centered Cubic (BCC) unit cells in x, y, and z directions have been considered. The results show that 250000 elements for one-quarter of the lattice structure are quite enough to obtain acceptable results. The effect of prescribed parameters on the load-displacement curve of the lattice structure has been studied. Based on the obtained results, diameter and hardening behavior are the most influential parameters and the significant effect on load-displacement curve has been observed.

In the current research, a three-dimensional finite element model was considered to predict the mechanical behavior of Single Wall (SWCNTs) and Multi Wall Carbon Nanotubes (MWCNTs). Assuming the nonlinear elastic behavior of C-C bond in large strains, hyperelastic models were considered. Literature review revealed that the material parameters of the hyperelastic models have been determined from the uniaxial tension loading, although the nonlinear elastic behavior is not identical in the tension and compressions. Thereby, the energy-stretch curve of C-C bond was determined from the second-generation Brenner potential in uniaxial tension and compression conditions. The results were fitted to the Ogden, Moony-Rivlin, and Yeoh hyperelastic strain energy functions to derive the material parameter of the mentioned models. The results indicated that the second order Ogden model could describe the tensile and compressive hyperelastic behavior of the C-C bonds accurately. The results of SWCNT bending showed that a unique response could be captured by considering the tension and compression simultaneously in deriving of the material parameters. From the results of SWCNT, the mechanical behavior of MWCNTs were predicted by assuming the Van der Waals bonds between the layers using the Lennard-Jones potential. Results of loading on the external layer of MWCNTs showed that an increase in the layers causes a decrease in the stress so that the stress-strain curves become identical beyond 8 layers. Accordingly, the material parameters of the first order Ogden model were determined for MWCNTs considering the simultaneous response in tension and compression.